Isotopic evidence for the tangled mechanism of the CO-PROX reaction over mixed and bare cobalt spinel catalysts. Issue 18 (17th August 2022)

• Record Type: Journal Article
• Authors: Hudy, Camillo; Gryboś, Joanna; Steenbakkers, Kim; Góra-Marek, Kinga; Zasada, Filip; Sojka, Zbigniew
• Is Part Of: Catalysis science & technology. Volume 12:Issue 18(2022)
• Page Start: 5723
• Page End: 5741
• Publication Date: 2022-08-17
• Subjects: Catalysis -- Periodicals; 541.395
• DOI: 10.1039/d2cy01063a
• Languages: English
• ISSNs: 2044-4753

Abstract

Abstract : The catalytic performance of the bare Co3 O4 and mixed cobalt-spinel catalysts (M x Co3− x O4 ; M = Cr, Mn, Fe, Ni, Cu, Zn) in the CO-PROX process was investigated in the temperature-programmed surface reaction (TPSR) mode using 18 O2 as an oxidant. Abstract : The catalytic performance of the bare Co3 O4 and mixed cobalt-spinel catalysts (M x Co3− x O4 ; M = Cr, Mn, Fe, Ni, Cu, Zn) in the CO-PROX process was investigated in the temperature-programmed surface reaction (TPSR) mode using 18 O2 as an oxidant. The developed heuristic approach, where the prototype isotopic compositions of the reaction products (C 16 O 18 O, C 16 O2, C 18 O2, H2 16 O and H2 18 O), inferred from a conceivable molecular course of the postulated catalytic scenarios, are confronted with the experimental data allows for delineation of the CO-PROX reaction mechanism. For this purpose, in addition to mixed spinels, several intentionally labeled isotopic 18 O2 /Co3 18 O4, 16 O2 /Co3 18 O4, 18 O2 /Co3 16 O4 reference CO-PROX systems were examined. It was shown that the catalytic turnovers of CO and H2 result from various combinations of the generic intrafacial Mars van Krevelen and suprafacial Langmuir–Hinshelwood/Eley–Rideal patterns, where the formation of surface carbonates as a common key intermediate allows for successful reproduction of the observed variation of the isotopic composition of CO2 and H2 O with the selectivity. The mechanistic proposals were substantiated by DFT+U and ab initio thermodynamic modeling, corroborated by IR studies, which provided the requisite theoretical background for the dual role of the carbonate species as intermediates or spectators in the CO-PROX reaction, depending on their mode of attachment on the catalyst surface.